Organopolysiloxanes with terminal reactive groups have considerable technical and industrial importance. Of particular interest from a practical point of view are such siloxanes which are equilibrated by the incorporation of sulfate groups into the siloxane structure. The term "equilibration" in this context refers to the equilibrium adjustment of the polysiloxane mixture in respect of the molecular weight distribution and the distribution of the different organosiloxane units which may be present within the molecule. The sulfate groups which are incorporated into the siloxane structure may also take over the function of a terminal reactive group. The chemical literature, including the patent literature, contains ample references to such systems. Examples are German Offenlegungsschrift No. 2 059 546 and German Offenlegungsschrift No. 2 059 554, to which particular attention is directed.
German Offenlegungsschrift No. 2 059 546 is directed to a procedure for the preparation of predominantly linear equilibrated organopolysiloxane mixtures containing terminal sulfuric acid groups. The equilibrated organopolysiloxane mixtures of the German Offenlegungsschrift can be represented by the general formula ##EQU7##
In this formula, the letter n stands for a value of 2 to 20 while R is a hydrocarbon group which in some cases may be substituted by a group which is inert to sulfuric acid. A portion of the hydrocarbon groups R may be replaced by the group ##EQU8##
The substances of formula I above are in equilibrium with cyclic compounds of the general formula ##EQU9## and sulfuric acid.
IN formula II above, R has the above indicated meaning while two of the groups ##EQU10## may be replaced by one group ##EQU11## In formula II, m has a value of from 1 to 10, preferably 1 or 2.
The subject matter of Offenlegungsschrift No. 2 059 554, as mentioned above, is a process for the preparation of equilibrated mixtures of polydiorganosiloxanylsulfates of the general formula ##EQU12##
In this formula, n has a value of 2 to 20, preferably 2 to 10, while m has a value of 1 to 10, preferably 1 to 2; the R groups may be the same or different and indicate lower alkyl of preferably 1 or 2 carbon atoms which, if desired, may be substituted. A portion of the R groups may be replaced by aromatic groups, preferably by phenyl, or by the group ##EQU13##
According to the Offenlegungsschrift, two of the R groups may be relaced inter- or intramolecularly by one group ##EQU14##
Of particular interest in this context are those organopolysiloxanes which, in addition to the siloxanyl sulfate groups, also contain terminal silylhalide groups, particularly silylchloride groups. The production of such compounds has been disclosed, for example, in German Pat. No. 1 174 509 and in U.S. Pat. No. 3,115,512. The presence of the siloxanyl sulfate groups assures the rapid and finite formation of the equilibration condition. Compounds of the nature referred to above are widely used starting compounds for numerous reactions. Thus, for example, they are used as starting compounds in the production of polysiloxanes with terminal hydroxyl groups or of polyalkyl silicic acid esters, of polysiloxanes with acyloxy alkyl groups and the like. They also serve as the organosilicon starting compounds for the modification of, for example, epoxy resins.
Of particular interest from a practical point of view are the reactions with higher molecular hydroxyl compounds for the production of polysiloxane-polyoxyalkylene-mixed block polymers as, for example, disclosed in the aforementioned U.S. Pat. No. 3,115,512. In such reactions, a tendency to side reactions can be observed. This tendency has is genesis in the reaction of the liberated sulfuric acid with the organic hydroxyl compounds under formation of sulfuric acid esters. This side reaction can be retarded and negated by the use of acid acceptors. However, from a practical point of view, it has been observed that in many instances and in spite of the use of acid acceptors, precipitation of small amounts of byproducts takes place.